Monoclonal antibody (MAb) conjugated fiber optic sensors will be developed. These biosensors are predicted to offer high sensitivity, simplicity of design and operation, and low costs. The contractor will investigate the feasibility of a biosensor which has the potential to detect various types of toxins, chemical contaminants, specific gases, and biological hazards. Coupler sensors are based on the remarkable sensitivity which fused single mode fiber couplers show to changes in refractive index. Initially, MAb coated biosensors will be used to document sensitivity, specificity, accuracy, and dynamic nucleotide probes for detecting microbiological contaminants. Coupler sensors are proposed as warning devices which would signal contamination of habitable areas, personal monitors for monitoring the extent of individual exposure, and as a sensitive quantitative all-optical assay for determining minute concentrations of toxins. The proposed sensor will be very inexpensive and safe and require minimal battery power for personal, field, or remote use.